Tillage and soil quality Tillage practices for sustainable agriculture and environmental quality in different agroecosystems

For centuries tillage has been used to prepare suitable seedbed to grow crops, and to control weeds and incorporate fertilizers, pesticides, manures and other amendments. In early years conversion of native ecosystems by tillage helped to unlock nutrients stored in soil organic matter, and thus `mine' naturally fertile soils to grow crops with minimum inputs for the growing population. However, at the same time, tillage was insidiously destroying soil organic matter and soil structure, and in this way, accelerating soil erosion and breaking the web of soil life itself (Papendick and Parr, 1997). The results of exploiting agricultural systems without consideration of the consequences of soil degradation caused by soil preparation are evident in those regions where soil is cultivated intensely and continuously (Derpsch and Moriya, 1998). Soil inversion and pulverization by repeated tillage accelerates decomposition of organic matter thus affecting soil physical, chemical and biological properties, the key attributes of soil quality (Cannell and Hawes, 1994). For the past thirty years, land management systems have been developed that minimize the need for soil tillage. Techniques such as no-tillage leave plant residues on the surface, protecting the soil from erosion. Many studies have shown that with continuos no-tillage soil organic matter increases, soil structure improves, soil erosion is controlled, and in time crop yields increase substantially from what they were under intensive tillage management (Cannell and Hawes, 1994; Papendick and Parr, 1997; Reeves, 1997). There is overwhelming evidence from several scienti®c studies that continuos no-tillage is the most effective and practical approach for restoring and improving soil quality, which is vital for sustained food production and a healthy environment. No-till farming has gained wide acceptance in Australia and North and South America but although the advantages of no-tillage are widely recognized, adoption of this technology has been very slow elsewhere. In May 1996, the International Soil and Tillage Research Organization (ISTRO) Board proposed and agreed to organize a symposium on Tillage and Soil Quality as a part of its 14th ISTRO Conference held in Pulawy, Poland from 27 July to 1 August, 1997. I was asked by the Secretary-General, Warren Dick to organize this symposium. The objective of this symposium was to invite and bring together scientists working in soil tillage research in different parts of the world and to deliberate and discuss their ®ndings in relation to the impact of different tillage systems on soil properties, crop production and environmental quality. After the Soil & Tillage Research 53 (1999) 1±2